Why Stephen Hawking Believes Humans Must Leave Earth

Confined to a wheelchair, physicist Stephen Hawking has roamed the universe in his mind. He'd like to see his fellow humans leave Earth physically—and soon.

"I believe what makes us unique is transcending our limits," Hawking said. That's why he takes part in the Breakthrough Initiatives, a suite of projects designed to help Earthlings find alien intelligence and visit the nearest neighboring solar system with a probe the size of a credit card propelled by a giant laser beam.

"How do we transcend these limits? With our minds and our machines," Hawking said. "The limit that confronts us now is the great void between us and the stars, but now we can transcend it." It's still not easy, of course, but we've now reached the point where we can at least design a system that could travel at a quarter of the speed of light, rather than the slow crawl that has limited every spacecraft built to date.

"I believe that the long-term future of the human race must be in space," Hawking said in a separate interview, with Charlie Rose. He says that humans have created their own extinction risk, and that staying on Earth is like keeping all our eggs in one basket. "Let's hope we can avoid dropping the basket until we can spread the load."

And besides, if everything goes smoothly, it could be more fun. "We are human, and our nature is to fly," Hawking said.